Well bore completion method



D. L. HARLAN ETAL WELL BORE COMPLETION METHOD Feb. 6, 1962 Filed Dec.30. 1959 2 Sheets-Sheet 1 Feb. 6, 1962' D. L. HARLAN ET-AL WELL BORECOMPLETION METHOD Filed Dec. 30. 1959 2 Sheets-Sheet 2 TRIAL- llnitetliStates This invention relates to a method of preparing a well bore priorto initiation of a procedure for the recovery of hydrocarbons containedin an underground formation. More particularly, it relates to a methodof preparing a Well bore which contains a column of oil to make theinitiation of a thermal recovery procedure relatively safe.

Recovery procedures in which a combustion-supporting gas such as oxygenor air is used to either drive the oil from the formation or to supportin situ combustion arehazardous from the standpoint of explosions in thewell bore caused by the accidental ignition of combustible mixtures offluid hydrocarbons and the combusdon-supporting gas. Such explosionscause damage to expensive well producing equipment and in some casescause harm to personnel and equipment at the surface above the well.Thus, it is necessary for the safety of personnel and equipment toremove oil from the well bore before initiating recovery processeswherein a combustion-supporting gas is injected into the well. In theprocess of removing the standing volume of oil from the well, water orother non-combustible, heavier-than-oil liquid is desirably utilized tolift the oil from the well bore. However, when the oil is removed inthis manner, a large volume of water is left in the well bore and thesurrounding formation. It is generally believed that the introduction ofwater into the hydrocarboncontaining formation is harmful to theformation from the standpoint of the production of hydrocarbons.

In accordance with the present invention, the method of preparing a wellbore containing a standing volume of oil for a secondary recoveryprocess in which a combustion supporting gas is introduced through thewell bore into a surrounding underground hydrocarbon-containingformation, and said recovery process employs producing equipmentincluding a'tubing string having fluid-tight well sealing means,generally referred to as a packer aflixed at a point along its length,comprises inserting said tubing string into the well bore, introducing anon-combustible heavier-than-oil liquid into said well bore in an amountsufficient to raise the oil-noncombustible liquid interface to a leveljust above that at which the packer will be set for the recoveryprocess, setting said packer at the desired level for the recoveryprocess, introducing a non-combustible fluid into the well bore abovethe packer whereby substantial pressure :is exerted downwardly againstthe packer, and initiat-- ing said secondary recovery process in theformation adjacent the lower portion of the well bore. The heavier--than-oil, non-combustible liquid is preferably water or .close to thebottom of the well bore and the liquid is introduced at the bottom ofthe well bore through the tubing string. When the Oil-liquid interfacereaches "the required level, the tubing string is lifted until theproducing equipment is at the desired level and the packer is set-toprovide a fluid-tight seal in the annulus formed between the well casingand the tubing string.

Non-combustible fluids which are used to pressurize the-packer-include,for example, inert gases such ,is ,nitroatent gen, which is injectedinto a well bore properly sealed at the well head, carbon dioxide orgases consisting principally thereof, and water and liquids consistingprincipally thereof such as brine. Oil lifted to the annular space abovethe Well sealing means does not constitute a hazard when employing inertgas to pressurize the annular space above the packer. Inert gas such asnitrogen is advantageously used in instances when it is undesirable'topermit water or brine above the packer to go into the formation when thepacker is unseated.

When introducing water or other similar liquid into the well bore abovethe packer it is desirable to inject it below the oil-water interface bymeans of tubing or hose inserted in the annulus of the well bore. Thishelps prevent the formation of emulsion and keeps the water and oil inseparate phases. Water is continuously introduced until the entirecolumn of oil is removed at the well head.

The position of the packer is determined by the final position of theproducing equipment hanging below the sealing means. This is necessarilyso since the distance between the packer and the equipment below it isfixed at the time it is lowered into the well.

A more complete understanding of the invention will result from readingthe following specification in conjunction with the'accompanying drawingin which:

FIG. 1 is a diagrammatic sectional view of a well bore containingequipment in position for the initial steps of the invention.

FIG. 2 is a diagrammatic sectional view of the well bore and equipmentof FIG. 1 having the equipment in position for the final steps of theinvention.

FIG. 3 is another diagrammatic sectional view of a well bore containingother equipment for thermal recovery positioned for the initial steps ofthe invention; and

FIG. 4 is a diagrammatic sectional view of the well bore of FIG. 3showing the equipment positioned for the final steps of the invention.

In FIG. 1, producing equipment has been placed in well bore 2 havingcasing 4 and casing shoe 6. The equipment has been assembled so that thelower end of tubing string 8, having perforations 10, is at or near thebottom of the Well bore 2. The Well bore 2 as shown in FIG. 1 contains astanding column of oil 12 having oil-gas interface 14. Thus, tubingstring Shaving its lower end near the bottom of the well bore can beused as a means to discharge or inject a fluid at the bottom of thecolumn of oil 12. Packer 16 is shown unset and positioned as low aspossible in the casing ,4.

A non-combustible liquid which is heavier than oil, such as water, ispumped down tubing 8 and injected through perforations 10 at the bottomof the column of oil 12. The injection of water is continued .until thecolumn of oil is lifted to a place-in the well bore where the oil-waterinterface is just above the level at which the packer is to be set forthe initiation of a thermal recovery procedure. The position of thepacker is determined by the desired position of the producing equipmenthanging below it. In the arrangement shown in FIGS. 1 and 2 in 'Whichthe equipment is designed for an in situ combustion procedure whereincombustion is initiated spontaneously by the introduction of chemicals,it is desirable to position the lower end of the tubing string justinside the casing 4. Thus, when oil-Water interface reaches the levelshown by dotted line 18 in FIG. 1 and line 20 in FIG. 2, tubing string 8is moved upwardly to place the lower end thereof in the desired positionwithin casing 4 and consequently positioning packer 16 just below oil-Water interface 20 in FIG. 2.

Packer 16'is set to provide a fluid-tight seal and water is introducedthrough opening 22 ofcasing 4. The preferred method of introducing waterinto the annulus formed by tubing 8 and casing 4 above set packer 16 isthrough a small tubing 24 inserted into the annulus and reaching to alevel beneath interface 20 so that the water is injected with littleturbulence beneath the interface. This method prevents the formation ofemulsions and maintains separation of oil and water while the water column slowly displaces the oil through opening 22 at the top of the casing4.

It has been found that in some instances it is not necessary to have thesmall tubing 24 inserted in the annulus to a level beneath interface 20.Water has been successfully injected into the annulus with the smalltubing 24 inserted only about 10 to feet below the well head at opening22. In this case, the water efficiently gravitated in the annulus to thepacker 16 and effectively raised and displaced the oil out of opening22.

When the oil has been removed from the annulus, water injection isterminated leaving a standing column of water over packer 16.

-As previously stated, there are times when it is undesirable topressure packer 16 with water. Therefore, an alternate method ofpressurizing the packer 16 is to inject an inert gas into the annulusabove the packer while maintaining a reason-ably gas tight seal at thewell head. The oil-column located in the annulus above the packer willadd to the pressure on the packer without hazard.

The method of completing a well for. recovery operations employing acombustion-supporting gas wherein downward pressure is applied to afluid-tight seal in the well bore, is disclosed and claimed in copendingapplication S.N. 863,044, filed of even date herewith by Charles D.Woodward and Billy H. Towell.

The well bore is now ready for the preparation of the formation for anin situ combustion process or other thermal recovery process using airor other combustionsupporting gas as a drive to force hydrocarbons fromthe formation.

In preparing the hydrocarbon-bearing formation for an in situ combustionprocedure, air is pumped through the tubing string 8 into the well borebelow packer 16. The initial volume of air entering the well bore drivesthe relatively small amount of water therein into the formation.Thereafter sufiicient pressure is supplied to establish permeability toadjacent well bores traversing the formation. As previously discussed,the mixture of a combustion-supporting gas and fluid hydrocarbons in theconfinement of the well bore is hazardous. The oil which was displacedby Water from the well bore was removed because of this hazard. It wasremoved by the method employed in order to prevent too much water fromgoing into the formation and to complete the well in a manner designedto reduce the possibility of a downhole explosion. Any explosion in therelatively small diameter tubing string would be inconsequential and anexplosion occurring in the annulus below the packer would be effectivelydampened by the pressurized packer.

When permeability has been established in the formation, in situcombustion is established by either mechanical or chemical means. Theequipment shown in FIGS. 1 and 2 is used for in situ combustioninitiated by chemical means. The equipment shown in FIGS. 3 and 4 can beused for thermal recovery processes wherein heating or ignition iscaused by mechanical heaters such as gas fired or electrical resistanceunits. In FIGS. 3 and 4, the apparatus differs principally from thatshown in FIGS. 1 and 2 by the inclusion of a heater or ignitor 26positioned around and at the lower end of tubing string 8. Heater 26, asshown is electrically powered by means of power cable 28 which runsthrough packer 16 without impairing its ability to produce a fluid-tightseal. After injecting sufiicient water at the bottom of the well bore toraise the oil-water interface to a level high enough to allow packer 16to be set just below the interface after the heater 26 is placed in thedesired position for the in situ combustion procedure, the packer is setand fluid is introduced above the packer. When hazard of explosion hasbeen reduced, air or other combustion-supporting gas is injected intothe lower portion of the well bore through tubing 8. The introduction ofair pushes the water remaining in the lower well bore into the formationand the continued air'injection establishes permeability through theformation to adjacent production well bores. Power is transmittedthrough cable 28 to the heater 26 which becomes heated to a temperaturesufficient to ignite the hydrocarbons near the well bore to establishcombustion.

The following is an example of the process of this invention forinitiating an in situ combustion by chemical means as performed in aproducing well in the Western United States. 1

' Example The producing string of the well was removed and the wellcleaned out to its total depth. Clean tubing, with perforated nippleattached to the lower end of the tail pipe was run into the well forabout feet. A check valve was included in this length of tubing. Apacker was assembled with the tubing at this point and the tubing wasthen run to within one foot of the bottom. Fifty barrels of water wascirculated into the tubing, raising the oil-water interface to a pointabove the final packer setting. The tubing was lifted placing the end ofthe tail pipe opposite the casing shoe (3343 ft.) and the packer was setjust beneath the oil-water interface at 3178 ft. The annulus 1above thepacker was filled with water to remove all the oi Air was injectedthrough the tubing string into the lower portion of the well using a lowstage compressor. The well head pressure had stabilized within 24 hoursat about 250 p.s.i. and the well was taking air at the rate of 200,- 000standard cubic feet per day. Adjacent wells were monitored for gas andair production. For the next five days air was injected at the rate of400,000 cubic feet per day at a well pressure of 240 p.s.i. After thefirst 3 days of air injection the closest adjacent well began to producegas. 0n the fifth and sixth days five other adjacent wells wereproducing gas. Air injection was stopped after the sixth day. Afterabout seven days the gas production of all the adjacent wells returnedto normal. The well was purged with nitrogen injected through the tubingstring. Thereafter, formation water was injected at a volume equal tothe borehole and four barrels of chemicals (fatty acid extract fromlinseed oil) were pressured down the tubing string. The extract wasdisplaced from the tubing string with nitrogen and the borehole waspurged with nitrogen. Air injection was commenced through the tubingstring at a rate of about 100,- 000 standard cubic feet per day and,after about three hours, well head injection pressure was steady atp.s.i. At this time the pressure rose sharply to p.s.i. and remainedconstant. After seven days the air injection rate was raised to 430,000standard cubic ft./ day and the well head injection pressure was 240p.s.i. Gas production from one adjacent well increased from 2000standard cubic feet per day to about 14,400 s.c.f./d. The gas productionfrom another adjacent well doubled and the oil production from the samewell rose from 40 to 54 bbls./day. Five days later another adjacent wellwas producing gas at 17,000 s.c.f./d. from a normal 1,750 s.c.f./d.Another adjacent well which was not producing measurable quantities ofgas prior to the injection of chemicals (linseed oil) now produced76,000 s.c.f./d. Still another adjacent well increased oil productionfrom 2 to 11 bbls./ day. The preparation of the injection well inaccordance with the invention prior to combustion produced a safer andmore convenient well bore for the establishment and maintenance of thesecondary recovery operation described in the foregoing example.

Obviously many modifications and variations of the invention, ashereinbcfore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

1. In the recovery of hydrocarbons contained in an underground formationtraversed by at least one well bore and where a combustion-supportinggas is injected into the formation through a tubing string positioned insaid well bore, said tubing string having a packer aflixed at a pointalong its length, the method of preparing said well bore containing acolumn of liquid hydrocarbons for the recovery operation which comprisesintroducing a noncombustible, heavier-than-oil liquid into said wellbore while maintaining the packer aflixed to the tubing string in aretracted position in an amount sufficient to raise theoil-non-combustible liquid interface to a level just above that at whichthe packer is to be set for said recovery operation, raising the tubingstring and packer afiixed thereto and, setting said packer below thelevel of said liquid interface to form a fluid-tight seal between thetubing string and the wall of the well bore at the desired level for therecovery operation, introducing a non-combustible fluid into the wellbore above the set packer whereby substantial pressure is exerteddownward against the packer, providing a combustion-supporting gas tosaid well bore below the set packer to drive the relatively small amountof non-combustible, heavier-than-oil liquid remaining in this part ofthe Well bore into the formation and to establish permeability toadjacent well bores traversing the formation, and initiating saidrecovery operation in the formation adjacent the lower portion of thewell bore.

2. In the recoveryof hydrocarbons contained in an underground formationtraversed by at least one well bore and where a combustion-supportinggas is injected into the formation through a tubing string position insaid well bore, said tubing string having a packer aflixed at a pointalong its length, the method of preparing said well bore containing acolumn of liquid hydrocarbons for the recovery operation which comprisesfirst inserting said tubing string into the well bore, the lower end ofsaid tubing string being positioned substantially at the bottom' of saidwell bore, introducing a non-combustible, heavierthan-oil liquid at thebottom of said well bore through said tubing string while the packerafiixed thereto is maintained in retracted position in an amountsufiicient to raise the oil-non-combustible liquid interface to a leveljust above that at which the packer is to be set for the recoveryoperation, raising said tubing string to the desired level for therecovery process, setting said packer in fluid-tight sealing arrangementbetween the tubing string and the wall of the well bore below saidliquid interface, introducing a non-combustible fluid into the well boreabove said packer whereby substantial pressure is exerted downwardlyaaginst the packer, introducing a combustion-supporting gas underpressure into the well bore below the set packer to drive theheavier-than-oil liquid remaining in the lower portion of the well boreinto the formation and to establish permeability to adjacent well borestraversing the formation, and initiating the recovery operation in theformation adjacent the lower portion of the well bore.

3. The method of preparing a well bore of claim 2 wherein thenon-combustible, heavier-than-oil liquid is an aqueous liquid.

4. The method of preparing a Well bore of claim 2 wherein saidnon-combustible fluid is an inert gas.

5. The method of preparing a well bore of claim 2 wherein saidnon-combustible fluid is an aqueous liquid.

6. The method of preparing a well bore of claim 5 wherein the aqueousliquid is introduced into the well bore above said set packer and belowthe oil-non-combusible liquid interface.

7. In the recovery of hydrocarbons contained in an underground formationtraversed by at least one Well bore and where air is injected into theformation through a tubing string positioned in said well bore, saidtubing string having a packer aflixed at a point along its length, themethod of preparing said well bore containing a column of liquidhydrocarbons for an in situ combustion operation which comprises firstinserting said tubing string into the well bore, the lower end of saidtubing string being positioned substantially at the bottom of said wellbore, introducing an aqueous liquid at the bottom of said well borethrough said tubing string while maintaining the packer atlixed theretoin a retracted position in an amount suflicient to raise the oil-aqueousliquid interface to a.

level just above that at which the packer is to be set for the in situcombustion operation, raising said tubing string to the desired level tocarry out an in situ combustion operation, setting said packer belowsaid liquid interface to form a fluid-tight seal between the tubingstring and the wall of said well bore, introducing an aqueous liquidinto the well bore above said packer but below the oilaqueous liquidinterface, injecting air through said tubing string to drive the aqueousliquid below the set packer into the formation, and initiating in situcombustion adjacent said well bore in the hydrocarbon-containingformation.

8. The method of preparing a well bore of claim 7 wherein in situcombustion is initiated by the injection of a spontaneous ignition typechemical through said tubing string into the formation and thereafterinjecting air through said tubing string.

References Cited in the file of this patent UNITED STATES PATENTS

